The purpose of this study is to evaluate the effect of concentrated (25.7kcal/oz infant formula compared with standard (20kcal/oz) infant formula on weight gain, body composition, immunologic and virologic status, quality of life, and dietary intake in HIV-infected infants from birth to 6 months. An equal number of HIV-exposed but uninfected infants will receive standard (20 kcal/oz) infant formula and will serve as a comparison group for the infected infants who receive standard formula.